Cold-gas refrigerating apparatus



Oct. 6, 1959 Filed March 14, 1955 J. w; L.'K6HLER ETAL COLD-GAS REFRIGERATING APPARATUS 7 3 Sheets-Sheet 1 IN ENToR Jacob wiLLcm Laurens AGENT J. L. KCHLER ETAL 2,907,175

COLD-GAS REFRIGERATING APPARATUS Oct. 6, 1959 3 Sheets-Sheet 2 Filed March 14, 1955 Jacob WiLLam Laurens INVENTOR KdhLer. Herman Fok ker 6, 1959 J. w. L. KGHLER ETAL 2,907,175

- COLD-GAS REFRIGERATING APPARATUS Filed March 14, 1955 3 Sheets-Sheet 3 INVENTOR Jacob WiLLem Laurens KbhLer Herman Fokker.

United States Patent COLD-GAS REFRIGERATING APPARATUS Jacob Willem Laurens Kiihler and Herman Fokker, Em-

masingel, Eindhoven, Netherlands, assignors, by mesne assignments, to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Application March 14, 1955,'Serial No. 493,926 Claims priority, application Netherlands March 19, 1954 11' Claims. (Cl. 626) This invention relates to cold-gas refrigerating apparatus. As is well-known, in such apparatus a gas traverses a closed thermodynamic cycle, during which it is invariably in the same state of aggregation, the apparatus comprising a space of lower temperature and a space of higher temperature. The volumes of the said spaces are influenced by bodies adapted to reciprocate substantially harmonically with a constant diflerence in phase, the spaces communicating with one another by way of a channel including a freezer, a regenerator and a cooler.

Such cold-gas refrigerating apparatus are frequently termed refrigerators operating on the reversed hot-gas piston motor principle. Said apparatus obtaining in one step a comparatively great difference in temperature, for example of 100 C. However, it is also possible to obtain a greater difference in temperature, for example of 250 C., so that the apparatus produces cold, for example, at 200 C. v

Cold-gas refrigerators may be designed in difierent ways, for example as displacer apparatus, as doubleacting apparatus, or as apparatus of which the cylinders are at an angle with one another.

In the regenerator of the apparatus the gas is heated when flowing from the cold side to the hot side and cooled when flowing from the hot side to the cold side. The gas thus absorbs heat from the filling mass of the regenerator when flowing in one direction and gives off heat thereto when flowing in the other direction. As is well-known, the gas cannot exchange so much heat with the regenerator that the difference in temperature between the cold and hot terminal surfaces of the regenerator is bridged completely. Upon leaving the regenerator at its cold side, the gas thus has a temperature higher than that of the cold terminal surface and at its hot side a temperature lower than that of the hot terminal surface.

This circumstance results in the regenerator loss. This loss may be regarded as if heat is transported by the gas from the hot side of the regenerator to its cold side or cold is transported from the cold side of the regenerator to its hot side.

It is already known that the regenerator loss, which is disadvantageous more particularly in cold-gas refrigerators, may be decreased by providing elements in the filling mass of the regenerator, through which the gas flowing through the regenerator is in heat-exchanging contact with a medium which is independent of the cycle in the refrigerator, which medium has a temperature lower than that which would prevail at the heat-exchanger. The term medium independent of the cycle in the apparatus is to be understood in this specification to mean a medium which does not take part in the thermodynamic cycle in the refrigerator at the time it is in heat-exchanging contact with the additional heat-exchanger.

According to the invention it has been found that particular results may be obtained if the cold-gas refrigerator comprises an additional space of variable volume which is connected to a predetermined part of the working space in the apparatus.

2,907,175 Patented Oct. 6, 1959 "ice least one additional space, of which the volume is also varied substantially harmonically, preferably by means of a piston-like body, the variations in volume of the additional space leading in phase with respect to the variations in pressure which occur if the volume of the additional space is constant and minimum.

The term leading in phase of the volume variations of the additional'space with respect to the variations in pressure is to be understood to mean that the minimum volume of the additional space, measured on the circle of the crank, occurs at the most 180 earlier than the maximum pressure. Due to the phase diiference, sub'- stantially expansion occurs in the additional space, so that heat is supplied from the regenerator to the said space, thus decreasing the heat exchange loss.

According to another aspect of the invention, the por-' tion of the communication channel located between the cold and hot terminal surfaces of the regenerator is connected to at least one additional space, of which the volume is also varied, preferably by means of apistonlike body, a constant phase difference, which may be adjustable, if desired, prevailing between the variations in volume of the additional space or spaces and those of the other space or spaces, and an additional heat-exchanger being provided at the connection between the additional space and the communication channel. w

This embodiment thus utilizes an additional heatexchanger in which the gas in the apparatus is in heatexchang ing contact with a medium which is independent of the cycle in the apparatus.

The additional heat-exchanger may be arranged in different ways. It is possible, for example, that a connection between the additional space and the communication channel includes the additional heat-exchanger. In one advantageous embodiment of the invention, the heatexchanger is located in the regenerator. In this embodiment the additional heat-exchanger may be arranged the filling mass of the regenerator, but it'is also possible for the heat-exchanger to be located between two portions of the regenerator. When reference is made to the hot and the cold terminal surface of the regenerator, they are to be understood to mean the terminal surfaces of the regenerator connected to the cooler and the freezer, respectively, of the cold-gas refrigerator. If the variations-in volume of the additional space lead in phase with respect to the variations in pressure in the refrigerator, which occur if the volume of the additional space is constant and minimum, substantially expansion occurs in the said space. However, if the variations in volume of an additional space lag in phase with respect to the variations in pressure, substantially compression occurs in the said space. i 7 p In one embodiment of the invention, the variations in volume of the additional space lead in phase with respect to the variations in pressure, which occur if the volume of the additional space is constant and a minimum, a medium independent of the cycle in the apparatus being cooled by the said additional heat-exchange f In another'embodiment of the invention, the variations in volume of the additional space lag in phase with respect to the variations in pressure which occur if the .volurne of the additional space is constant and minimum, a medium independent of the cycle in the apparatus being heated by the additional heat-exchanger.

In contra-distinction to the aboverdescribed cold-gas refrigerator of known type, the amount of heat supplied to the additional heat-exchanger or extracted therefrom is less dependent upon the output of the regenerator, the influence of the regenerator being smaller, so that the supply and extraction of heat is not primarily dependent upon the fictive thermal flow through the regenerator, but is dependent upon the expansion or the compression in the additional space.

If the cold-gas refrigerator is of a design such that substantially expansion occurs in the additional space, then in a further embodiment of the invention a communication for the medium independent of the cycle in the apparatus exists between the additional heat-exchanger and the freezer, so that this medium may be pre-cooled by the additional heat-exchanger before being cooled by the freezer.

If, however, the cold-gas refrigerator is of a design such that substantially compression occurs in the additional space, the cold-gas refrigerator is particularly suitable for use in gas-rectifying installations.

A method of fractionating mixtures of gases, for example air, to form fractions of different volatilities in a gasrectifying installation is characterized in that the installation comprises a cold-gas refrigerator and the mixture of gases to be fractionated is supplied at a suitable area to a gas-rectifying column in which the mixture of gases is fractionated, heat being extracted from the column by means of the cold-gas refrigerator and the additional heat-exchanger or exchangers being in heat-exchanging contact with at least one of the media associated with the gas-rectifying system.

In another method, the liquid of the highest boiling point is in heat-exchanging contact with an additional heat-exchanger, heat being supplied to the said fraction. This method may advantageously be used more particularly if atmospheric air is to be fractionated and the oxygen must be obtained in the liquid state.

In another method the gas-rectifying column is of the single type, so that more particularly a simple installation ensues.

The cold-gas refrigerator according to the invention may be of a design such that each additional space is varied by an associated piston-like body, coupled by way of an associated driving-rod system to the crank-shaft. A further and very simple construction in which the additional piston and the additional driving-rod system are not required ensues if, in one embodiment of the invention, the piston-like body acting upon the space of lower temperature comprises at least two portions of different diameters, which portions are adapted to reciprocate in associated cylindrical spaces, a space influenced by an annular surface formed by the transition between two portions of different diameters of the piston-like body constituting the additional space.

If in this construction the additional heat-exchanger is used for cooling a medium independent of the cycle in the apparatus, then in a further embodiment of the invention the variations in volume of the additional space are in the same phase with the variations in volume of the space of lower temperature.

If, however, the additional heat-exchanger is used for heating a medium, then in a further embodiment of the inevntion, the variations in volume of the additional space differ in phase by 180 from the variations in volume of the space of lower temperature.

In order that the invention may be readily carried into effect, it will now be described, by way of example, with reference to the accompanying drawing, in which Fig. 1 shows a cold-gas refrigerator comprising an additional heat-exchanger by which a medium of low temperature can be heated.

Fig. 2 shows a gas-rectifying installation comprising such a cold-gas refrigerator.

Fig. 3 shows a cold-gas refrigerator in which a medium can be cooled by means. of the heat-exchanger.

Fig. 4 shows a cold-gas refrigerator without an addi tional heat exchanger and,

Fig. 5 shows a heat-exchanger arranged outside the communication channel and between the spaces of higher and lower temperature.

The refrigerator shown in Fig. l is a cold-gas refrigerator of the displacer type. It comprises a cylindrical space bounded by a wall 1 and a cylindrical space bounded by a wall 2. A piston 3 and a displacer portion 4 are adapted to reciprocate with a substantially constant difference in phase in the space bounded by the wall 1. The displacer comprises a portion 5 which is adapted to reciprocate in the cylindrical space bounded by the wall 2, the portion 5 being of a diameter larger than that of the portion 4. The portion 5 of the displacer acts upon a space 6 provided above it. The space 6 constitutes the space of lower temperature and communicates via a freezer 7, a regenerator portion 8, an additional heat-exchanger 9, a second regeneration portion 10 and a cooler 11 with a space 12. The latter constitutes the space of higher temperature. The communication channel between the freezer 7 and the cooler 11 is thus occupied by a regenerator comprising two portions 8 and 10, a heat-exchanger 9 being provided between the said portions. The regenerator comprises a cold terminal surface 13, connected to the freezer, and a hot terminal surface 14, connected to the cooler. An additional space 15 is connected to the portion of the communication channel between the terminal surfaces 13 and 14, that is to say at the heat-exchanger 9. The volume of the additional space 15 is influenced by an annular surface 16, resulting from the difference in diameters of the portions 4 and 5 of the displacer. The variations in volume of the space 15 differ in phase by 180 from the variations in volume of the space 6. The displacer is coupled via a driving-rod system 17 to a crank of a crank-shaft 18, the piston being coupled via drivingrod systems 19 to cranks of the same crank-shaft. The refrigerator is driven by an electric motor 20. A driving rod system such as disclosed herein appears in US. Patent No. 2,465,139 to Van Weenen et al.

The freezer 7 is externally provided with fins 21 located in a condenser space 22 bounded by a wall 23 having heat-insulating properties. The space 712 has an inlet aperture 24 for the gas to be cooled, which may condense, if desired, on the fins 21, the condensate being collected in an annular channel 25 and discharged through a tube 26. The additional heat-exchanger 9 is externally provided with fins 27 and by means of this heat-exchanger it is possible to 'heat at this area a medium of a temperature lower than that of the temperature of the gas in the refrigerator. The medium may be supplied through a channel 28 and discharged through a channel 29. Cooling water may be supplied to the cooler 11 through conduit and discharged therefrom through conduit 136.

When the cold-gas refrigerator is driven by the electric motor 20, substantially expansion occurs in the space 6 due to a suitable position of the cranks of the crank shaft, whereas substantially compression occurs in the space 12. Consequently, heat is supplied to the freezer at a lower temperature [and heat is discharged from the cooler at a higher temperature. Compression also substantially occurs in the space 15, the volume of which, as mentioned before, is varied with a phase difference of with respect to the volume of space 6, and the heat produced as a result of the compression can be dissipated via the heat-exchanger 9. A detailed disclosure of the hot space and freezing space is set forth in US. Patent No. 2,657,553 to Jonkers, and the teaching of volume varying means is set forth in US. Patent No. 2,465,134 to Van Weenen et al.

If the freezer 7 has a mean temperature of, for example -200 C. and if the cooler 11 has a mean temperature of +50 C., the temperature prevailing in the space 15 is comprised between the above-mentioned temperaturesdependent upon the position of the heat-exchanger 9 in the regenerator. Due to the presence of the additional heat-exchanger 9, it is thus possible to evaporate a liquid of a low boiling point, for example oxygen, having a temperature of -183 C. at atmospheric pressure. This possibility enables the cold-gas refrigerator shown inFig. 1 to be used in a gas-rectifyinginstallation.

Fig. 2 shows a'gasqectifying installation employing such a cold-gas refrigerator. The installation comprises a gas-rectifying column 30, which is of the single type, and a cold-gas refrigerator 31. The mixture of gases to be fractionated, for example air, is supplied via a channel 32 which includes a pump 33, of which the overpressure may be low and sufiicient to overcome the resistance to flow of the mixture of gases in the installation. The mixture of gases then flows through a heatexchanger 34 in which it is cooled due to heat-exchanging contact with the fraction of the lowest boiling point produced in the installation, in this case the nitrogen. The mixture of gases thus cooled flows through a channel 35 to a heat-exchanger 36 which is included in a boiling vessel 37 of the column and in which the mixture of gases is cooled further due to heat-exchanging contact with the liquefied fraction of the highest boiling point which is contained in the boiling vessel and thus evaporates this fraction at least in part. The cooled mixture of gases is subsequently supplied through a channel 38 to the gas-rectifying column, in which it is fractionated, the fraction of the highest boiling point in the. liquid state being collected in the boiling vessel and the fraction of the lowest boiling point ascending as gas in the column, leaving the column through a tube 39 branched into two portions 40 and 41. The portion 40 is connected to the condenser space of the cold gas refrigerator in which this portion of the fraction is condensed, the condensate being supplied through a channel 42 to the gas-rectifying column in which it serves as a washing liquid. The part of the fraction discharged through the channel 41 is in heat-exchanging contact in the heatexchanger 34 with the mixture of gases to be fractionated and subsequently leaves the installation.

Since in the gas-rectifying installation air is fractionated, the amount of heat still present in the mixture of gases after the cooling by the fraction of the highest boiling point is not suificient to bring about the desired evaporation in the boiling vessel 37. An additional amount of heat may be supplied to the boiling vessel by means of the cold-gas refrigerator and for this purpose part of the fraction of the highest boiling point is led through a line 42a including a pump 43 connected to the channel 28 of the cold-gas refrigerator (see Fig. 1) to the additional heat-exchanger 9, in which this fraction evaporates, the vapour produced being supplied through a channel 44 back to the column. The residue of the liquid fraction of the highest boiling point may be discharged from the boiling vessel through a channel 45. It is thus possible with such a gas-rectifying column of simple construction to obtain the fraction of the highest boiling point in a manner which is economically justified.

Fig. 3 shows a further embodiment of the invention comprising a plurality of additional spaces whose variations in volume are in phase with those of the space of lower temperature.

In this embodiment also the refrigerator is of the displacer type. The displacer comprises three portions 50, 51, 52 of different diameters which are adapted to reciprocate in associated cylinders 53, 54, 55 respectively. The refrigerator also comprises a piston 56 which is also adapted to reciprocate in cylinder 53. The displacer and the piston reciprocate in known manner with a substantially constant difierence in phase and for this purpose they are provided with driving-rod systems as shown also in Fig. l. The portion 52 of the displacer acts upon the volume of a space 57, which is the space of lower temperature and which communicates via a channel including a freezer58, a first regenerator portion 59, a firstadditional heat-exchanger 60, a second regenerator portion 61, a second additional heat-exchanger 62, a third regenerator portion 63 and a cooler 64 with a space 65. The space 65 constitutes the space of higher temperature. The refrigerator comprises two additional spaces 66 and 67, the volumes of which are varied by means of annular surfaces 68, 69 respectively. The variations in volume of each of the said additional spaces are in phase with those of the additional space 57. The additional spaces 66, 67 communicate via the heat exchangers 60, 62, respectively, with the communication channel between the space 57 of lower temperature and the space 65 of higher temperature. Since variations in voiurne of the spaces 66, 67 are in phase with those of the space 57, substantially expansion occurs also in the said additional spaces. Volume varying means, as stated before, are disclosed in US. Patent No. 2,465,139 to Van Weenen et al. The freezer 58 is externally provided with fins 70 for condensation of a medium which can be collected in an annular channel 71. The heat exchangers 60 and 62 are externally provided with fins 72, 73, respectively. Cooling liquid, for example water, may be supplied to the cooler through a channel 74 and be discharged therefrom through a channel 75. The upper portion of the refrigerator is surrounded by a wall 76 having heat-insulating properties in such manner that a channel forms a medium to be cooled, which at first is in heat-exchanging contact with the fins 73 of the heatexchanger 62, then with the fins 72 of the heat-exchanger 60, and at last with the fins 70 of the freezer 58. Since the additional heat-exchangers are located in the regenerator between the cold terminal surface 77, connected to the freezer 58, and the hot terminal surface 78 of the regenerator, connected to the cooler 64, the temperatures of the additional heat-exchangers are comprised between those of the freezer and the cooler. A medium, for example air, flowing along the additional heat-exchangers is thus cooled in a stepwise manner. Due to the presence of the additional spaces, cold is now produced at a higher temperature than is the case in the space 57, resulting in an improved output of the refrigerator. The medium to be condensed can be discharged through a discharge line 79 including a liquid lock 80.

In the cold-gas refrigerator shown in Fig. 4, the regenerator does not comprise an additional heat-exchanger,

but the additional space communicates directly with the regenerator.

Thecold-gas refrigerator shown in Fig. 4 is also of the displacer type, the displacer comprising two portions 90, 91, which are adapted to reciprocate in associated cylinders 92, 93, respectively. A piston 94 can also reciprocate in'cylinder 92. Both the displacer and the piston comprise driving-rod systems to permit their displacement with a substantially constant difference in phase in a similar manner as shown in Fig. 1. The portion 91 of the displacer acts upon a space 95 of lower temperature, which communicates via a freezer 96, a first portion 97 of the regenerator, a second portion 98 of the regenerator and a cooler 99 with a space 100. The latter space constitutes the space of higher temperature in which substantially compression occurs, whereas suh stantially expansionoccurs in space 95. The refrigerator comprises an additional space 101, the volume of which may be varied by means of an annular surface 1&2 constituting the transition between the portions 91, 99 of the displacer, the variations in volume being in phase with those of the space 95. Consequently, sub stantially expansion occurs in the space 101, so that heat may be supplied thereto, thus permitting the reduction of regeneration loss of the refrigerator. The regeneration loss may be regarded as if heat flows from the hot terminal surface 103 of the regenerator to the cold terv minal surface 104 thereof, as a result of which the cold output of the refrigerator is decreased. Since substantially expansion occurs in the space 102, heat is extracted at the area at which the said space communicates with the regenerator, so that this fictive flow of heat can thus be intercepted. The cold production of space 95 is smaller than it could be with an ordinary displacer, but since the space 101 produces cold at a higher temperature, the output of the refrigerator as such is yet higher.

If the additional space 101 is constant and minimum, the variations in volume of the space 95 measured on the circle of the crank lead, for example by 20 with respect to the variations in pressure.

The variations in volume of the additional space 101 are in phase with those of space 95, so that the variations in volume of the additional space also lead in phase with respect to the variations in pressure. The refrigerator shown comprises in the usual manner a condenser space 105, to which a gas to be cooled may be supplied through an aperture 196, whereupon the gas can condense, if desired, and be collected in an annular channel 107 to be discharged through a tube 108.

Fig. shows diagrammatically a cold-gas refrigerator in which the additional heat-exchanger is not included in the regenerator. The cold-gas refrigerator shown in Fig. 5 comprises a space 110 of lower temperature which communicates via a freezer 111, a regenerator 112 and a cooler 113 with a space 114, which constitutes the space of higher temperature. The spaces are influenced by pistons 115, 116, respectively, which are coupled via driving-rod systems 117, 118, 119, 120, 121 and 122, 123, 124, 125, 126, respectively, to a crank 127 of a crankshaft 128.

The refrigerator comprises an additional space 129, the volume of which may be varied by means of a piston 130, coupled via a driving-rod 131 to a crank 132 of the crank-shaft 128, the angle enclosed by the cranks 132 and 127 being such that substantially expansion occurs in the space 129. The latter space communicates via an additional heat-exchanger 133 with the regenerator. Since substantially expansion occurs in the space 129', a medium can be cooled by means of the heat-exchanger 133. If the additional space 129 is constant and minimum, that is to say if the piston 130 is maintained in its upper position, the variations in volume of space 110 lead by 15, measured along the circle of the crank, with respect to the variations in pressure. The variations in volume of the space 129 now must lead by 0-l80 with respect to the variations in pressure. If a phase difference of, for example, 90 is chosen, the variations in volume of the additional space must lead by 90-l5 :75 with respect to the variations in volume of the space 110.

In the embodiment above-described, pistons serve to vary the volumes of the spaces. However, it is alternatively possible for the volumes of the spaces, more particularly for the volume of the additional space, to be varied by means of other elements such as membranes or bellows.

It is also possible to construct a cold-gas refrigerator so as to comprise a plurality of additional spaces, expansion substantially occurring in one or more spaces and compression substantially occurring in one or more other spaces. In this type of refrigerator it is possible, for example, to cool a medium which is independent of the cycle in the refrigerator, whereas another medium can be heated. If the refrigerator is of the displacer type, the displacer may be of a construction such that it occupies successively, counted from the space of the lower temperature, at first a portion of a small diameter, then one or more portions of steadily increasing diameters, and at last again one or more portions of small diameter.

The phase difference of the variations in volume of the additional space may be varied in known manner in the 8 embodiment of Fig. 5, so that the amount of heat or cold produced in the said space is varied. The phase difference may be varied, for example, by varying the po sition of the crank of the piston acting upon the additional space.

What is claimed is:

1. A cold-gas refrigerator in which a medium traverses a closed thermodynamic cycle, said medium being in the same state of aggregation; comprising a cylinder having a chamber of lower temperature and a chamber of higher temperature, at least two pistons reciprocating in said cylinder substantially harmonical-ly with a constant diflierence in phase and affecting the volumes of medium in said chambers, separate driving means for said pistons driving the same out of phase, a low temperature heat absorber, a high temperature heat rejector, and at least two regenerators provided with hot and cold terminal surfaces, said heat absorber, heat rejector and regenerators being connected in series and communicating with said chambers, a third chamber, and means operatively connecting said third chamber to said regenerators at a point located between said hot and cold terminal surfaces thereof, the volume of said additional chamber being varied by means of one of said pistons, the variation in volume of said third chamber leading in phase with respect to the variations in pressure which occur if the volume of the third chamber is constant and at a minimum.

2. A cold-gas refrigerator as set forth in claim 1 wherein there is a constant phase difference between the variations in volume of said chamber of lower temperature, said chamber of higher temperature, and said third chamber.

3. A cold-gas refrigerator as set forth in claim 1 wherein there is an adjustable phase difference between the variations in volume of said chamber of lower temperature, said chamber of higher temperature, and said third chamber.

4. A cold-gas refrigerator as set forth in claim 3 further comprising an additional heat exchanger located in the side of one of said regenerators.

5. A cold-gas refrigerator as set forth in claim 4 wherein the variations in volume of said third chamber lead in phase with respect to the variations in pressure which occur if the volume of the third chamber is constant and at a minimum, and a medium independent of the refrigerator cycle being cooled by said additional heat exchanger.

6. A cold-gas refrigerator as set forth in claim 5 fur ther comprising means for pre-cooling said independent medium before being cooled by said low temperature heat absorber.

7. A cold-gas refrigerator as set forth in claim 4 wherein the variations in volume of the third chamber lag in phase with respect to the variation in pressure which occur if the volume of the third chamber is constant and at a minimum, and a medium independent of the cycle in the refrigerator being heated by said additional heat exchanger.

8. A cold-gas refrigerator as set forth in claim 1 wherein one of said piston-like bodies acting upon said chamber of lower temperature comprises at least two portions of different diameters, said cylinder having correspondingly shaped parts, said space having as a boundary surface the transition between said portions of different diameters and constituting said third chamber.

9. A cold-gas refrigerator as set forth in claim 8 wherein the variations in volume of the third chamber are co-phasal with the variations in volume of said chamber of lower temperature.

10. A cold-gas refrigerator as set forth in claim 8 wherein a phase difference of exists between the variations of volume of the additional space and those of the space of lower temperature.

11. A cold-gas refrigerator in which a medium traverses a closed thermodynamic cycle, said medium being in the same state of aggregation comprising a cylinder, a piston and a displacer reciprocating in said cylinder and defining therewith a chamber of lower temperature and a chamber of higher temperature, separate driving means for said piston and displacer operating the same out of phase, said piston and displacer affecting the volumes of medium in said chambers, a high temperature heat rejector, a low temperature heat absorber, at least two regenerators, a heat exchanger positioned between and abutting said two regenerators, a third chamber located between and connected to said heat exchanger, and means connecting said third chamber to a point he- 10 tween the hot and cold terminal surfaces of said regenerators, the volume of said third chamber being varied by said displacer, the variations in volume of said third chamber leading in phase with respect to the variations in pressure which occur if the volume of a third chamber is at a minimum.

References Cited in the file of this patent UNITED STATES PATENTS 2,417,279 Van Nuys Mar. 11, 1947 2,423,273 Van Nuys July 1, 1947 2,465,139 Van Weenen et al Mar. 22, 1949 2,486,081 Van Weenen Oct. 25, 1949 2,657,553 Jonkers Nov. 3, 1953 

